The present invention relates to a system for monitoring the inflation pressure and anomalous temperature of rotating tires on a moving vehicle and in particular to a system for monitoring the pressure and temperature utilizing optoelectronic components located on the stationary structure of the vehicle and on an elastic diaphragm in the tire side wall or the wheel rim.
Pneumatic tires for automotive vehicles are designed for certain inflation pressures and load ranges. Both over inflation and under inflation can have consequences detrimental to tire life and performance. Over inflation can be avoided by the exercise of due care at the time of tire inflation. The only way to guard against prolonged periods of under inflation, however, is by frequently checking the pressure. The visual observation of a tire as an indicator of under inflation is not reliable, especially with radial tires. The manual checking of each of the four tires on an automobile with a tire pressure gauge is considerably more accurate than visual observation, but involves a considerable expenditure of effort. Experience has indicated that it is unrealistic to expect that a typical vehicle owner will perform this degree of maintenance on a frequent basis. At best, tire pressure checking will be done randomly, if at all.
The owners and operators of commercial vehicles and particularly fleets are affected on a much larger scale by under inflated tires and hence, are more prone to perform tire pressure checking on a more regular basis than most people do on their personal vehicle However, in the course of checking inflation pressures, there will doubtless be many tires that are found to be properly inflated and therefore, the time involved in checking these tires is an extra expense to the fleet owner. Several methods for measuring and transmitting tire inflation pressures to a vehicle operator have been reported in the technical literature. The tire inflation pressure measurement methods previously recorded fall into two categories: 1) those that require piercing of the tire rim; and 2) those that do not require piercing of the tire rim. Because pneumatic tires already have one hole pierced in the rim for the valve stem, the addition of a second hole in the rim for the inflation pressure sensor doubles the likelihood of leaks occurring. However, piercing of the tire rim is necessary for sensors that are attached to the exterior surface of the wheel, such as those commonly used in connection with magnetically coupled transmitters.
Magnetically coupled devices require a very small air gap between the rotating magnetics mounted to the rim and the stationary detector mounted to the vehicle structure in order for the device to work properly. The size of the air gap required is often less than one tenth of an inch. A further problem is that even small changes in the size of the air gap over time have a very significant affect on calibration of the system. It is difficult to establish and maintain such a small air gap due to variations in the run out, or evenness of the rim plane, from one wheel to another, and changes in the dimensions caused by variations in the ambient temperature.
Sensors that are attached inside the rim, or imbedded in the rubber side wall of the tire, do not require rim piercing. These sensors require radio frequency transmitters with rotating power sources attached to the wheel and a receiving antenna fixed to the nonrotating vehicle structure. Such devices add considerable complexity and cost to the system.
It is an object of the present invention therefore, to provide a tire pressure measuring and transmitting system which avoids the complexity of a radio frequency transmitter and power source mounted to the inside of the rim.
It is an advantage of the tire monitoring system of the present invention that in a preferred embodiment, additional piercing of the wheel rim is avoided.
It is a further advantage of the tire monitoring system of the present invention that the gap between the stationary sensor and the rotating tire need not be precisely controlled. This allows for normal variations between tires, rims and mounting structure.
The pressure measuring and transmitting system of the present invention utilizes an optical reflective indicator imbedded in the side wall of a tire and therefore does not require piercing of the rim. Optoelectronic emitter and detector assemblies are located on the nonrotating vehicle structure and therefore do not require power sources to rotate within the wheel. The method of data transmission by means of the optical reflective indicator in the tire side wall eliminates the requirement for the precise air gap used with the magnetically coupled devices. The emitting and receiving apparatus of the optoelectronic emitter and detector assemblies can be located further from the tire, one inch or more, and changes in the distance between the apertures and the tire do not effect calibration.
The system of the present invention consists of an inflation pressure indicator that is preferably mounted to the side wall of a tire and a laser diode emitter and detector assembly and electronics mounted to the nonrotating structure of the vehicle. The laser diode emits an electromagnetic signal, such as light radiation, that is reflected by the indicator back to the detector where the signal is processed by the system electronics and the tire pressure displayed to the vehicle driver. The system is operated in two modes, one mode is used to read the reflected signal for determining inflation pressure and in the other mode, the emitter is turned off and the overall infrared thermal emission from the tire side wall is read to identify tires with temperature anomalies.
The tire temperature monitoring is intended to provide primarily a warning of eminent danger. The most frequent occurrence involves one tire failure as opposed to all tires failing at the same time. Therefore, the system determines a temperature difference or anomaly between the tires rather than attempting to measure the tire absolute temperature which would require a much higher sensitivity for the detector in the longer wavelengths. The temperature sensing described herein identifies a tire whose thermal emission exceeds the average thermal emission of all tires by a specified amount.
As an alternative to placing an optoelectronic emitter and detector assembly at each wheel with an emitting diode and detector, a single light source can be used and transmitted to each wheel site through a fiber optic cable which terminates at a lens assembly whose aperture is oriented to illuminate the rotating pressure indicator. A second cable can be used to transmit the reflected signals to a central processing unit where the detectors are located.
Further objects, feature and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.